The present invention relates to a method for making a diaryl carbonate, such as diphenyl carbonate, by effecting the hydrolysis of a tetraaryl orthocarbonate.
Methods for making polycarbonates are constantly being evaluated. The route to polycarbonates by the melt transesterification of a diaryl carbonate often provides a significant environmental advantage over the reaction of bisphenols with phosgene under interfacial reaction conditions. In addition, polycarbonates prepared by melt transesterification have low levels of contaminants such as sodium and halide ions, and are therefore particularly suitable for use in optical applications such as for the manufacture of compact disks.
However, manufacture of polycarbonates by melt transesterification of diaryl carbonate has not been extensively exploited on a commercial scale. One reason why it has not been used more extensively is that a satisfactory synthesis for diaryl carbonate has not been developed.
For example, one procedure for making diaryl carbonates is based on a low conversion, multi-step melt transesterification technique employing a dialkyl carbonate and a phenol Another method employs phosgene with a phenol. A third procedure involves the direct carbonylation of phenol requiring a Pd catalyst which is difficult to recycle. As a result, additional procedures for making diaryl carbonates are of interest.
The conversion of tetraaryl orthocarbonates to diaryl carbonates is disclosed in Kandanarachchi et al., J. Chem. Soc., 1992, 777-778, and Kandanarachchi et al., J. Am. Chem. Soc., 116, 5592-5600 and 5601-5606 (1994). The reaction of carbon disulfide with a cuprous phenate to form a tetraaryl orthocarbonate is also known; reference is made to Narasimhamurthy et al., Tetrahedron Letters, 27,991-992 (1986). However, an integrated process for converting phenols to diphenyl carbonates via tetraaryl orthocarbonates does not appear to be known.